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EGR/Q-JETproblems ??? please help !!!!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by pilgrim, May 5, 2003.

  1. pilgrim

    pilgrim 1/2 ton status

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    My engine has been running poorly until on accident i unhooked the EGR. it was on manifold vac. then wham /forums/images/graemlins/smile.gif the idle smoothed right out. great but on the road it has a "soft-bucking" feel when you give it gas /forums/images/graemlins/confused.gif..

    does anybody know how an EGR works???(i know its a exhaust gas recirclator, but whats its exact function and could i block it off. why would it affect my idle quality?? /forums/images/graemlins/confused.gif

    my #6 plug was fouling (oil build up/crud) alot last year until i removed the head and found the exhaust valve to be bent a little. got it fixed and new oil seals to. now the plug is kinda fouled again /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif

    could hooking up the EGR to the wrong vac source be causeing all my problems. is the egr's location over #6 plug a related problem maybe??

    tell me what more info you need. i don't want to overload the question with useless facts /forums/images/graemlins/smirk.gif
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    EGR basically introduces "inert" gas (exhaust byproducts) into the mixture BEFORE it reaches the cylinders, to "false fill" the combustion chamber. Basically, since the EGR introduces inert gas, the mixture won't burn too lean if you reduce the amount of gas to the fuel/air mixture.

    EGR is designed to only work at cruise, not idle, not WOT, so when operating correctly has no adverse affect on power. However, when not working correctly, you can end up with poor idle/stalling, surging at times, and so on.

    Supposedly if you press up on the underside of the valve (your fingers will fit in there) when its cold, the operation of the diaphram should be smooth. Also, pushing up on the diaphram when idling should cause stalling as well.

    As I said, EGR is designed to work only at cruise, so the first step is to make sure it isn't hooked to the wrong vacuum port. Typical location is passenger side, midway up the front of the carb, but in the 80's, switches and what not were commonly "inline" with the EGR, vac advance, etc., so vacuum port location could be different or not present at all, depending on the individual application.
     
  3. pilgrim

    pilgrim 1/2 ton status

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    wow, very many thanks kind sir. as you noted, in some cases the EGR is hooked to a switch. it is that switch i removed a long time ago. thinking that it did nothing important. (insert "well that was dumb" statement here /forums/images/graemlins/smirk.gif)

    so since i no longer have this switch or even remember how things were hooked up. can i just leave it "unhooked" or will this cause some ill affect to my engine? maybe i need to get a non-egr manifold.

    heres something puzzleing.
    the bucking problem was never an issue when i had the EGR hooked up (wrong). after unhooking it all the other issues went away (stalling,poor idle etc..) but i got instead this bucking feel. so i hooked it back up the same old way to not only have the old problems back but the bucking was still there?? /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif. it would therefore seem somthing happened when i drove around with it unhooked for a week. just thinking out loud /forums/images/graemlins/smirk.gif

    thanks again /forums/images/graemlins/grin.gif
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Well, with EGR disconnected, and the carb "expecting" EGR, it's more than likely running lean at cruise, which will cause surging, for one thing.

    If you can hook it back up, do it, if not, you'll *probably* need to re-jet or re-rod the primaries. I did when I put the non-EGR engine in my truck, with a carb that was from an EGR application. You could really feel it at about 35MPH.

    And no, I wasn't trying to get around emissions devices, it was all I had when I put the truck together /forums/images/graemlins/smile.gif
     
  5. pilgrim

    pilgrim 1/2 ton status

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    i thought it might have to due with a lean/rich condition also. so useing a 1 watt O2 sensor i got readings of 550-870mv at cruise. which is north of the stoich 400mv. i was told its better to run rich, so i have left it alone. but the readings go bellow 400 and bounce all around when i step on the gas. since this is a brand new edelbrock Q-jet, could i just increase the fuel/air ratio since its ajustable?? rather then re-jetting.

    also if you know, how does it affect the carb if all of this is going on downstream of it?

    thanks for all the help, this has been hard to figure out /forums/images/graemlins/grin.gif
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    O2 readings aren't really that accurate unless you go with a wide-band. Accurate enough for an ECM, where the narrow band(?) O2 sensors basically act as an on/off for fuel supply.

    If you look at a chart with mixture/voltage readings of a narrow band O2 sensor, there is a VERY small percentage of time where voltage is actually near 14.7 and the corresponding voltage. If it was STUCK in one "range", then you'd have a real indicator, although your 550-870 readings are fairly consistent.

    Can't adjust cruise mix without opening the carb up.

    As for affecting the carb, if you mean hurting it to run the way it is, no it doesn't.
     
  7. pilgrim

    pilgrim 1/2 ton status

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    Re: EGR/Q-JETproblems ??? please help !

    /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif
     

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